The park is twice the size of the Grand Canyon and searchers described the area as "some of the roughest terrain we have in the state."

Five searchers have been injured in the rescue operation, including one who was bitten by a rattlesnake and had to be airlifted to a hospital where he remains in intensive care.

Family and friends of Herdman said they are hoping his outdoor experience and training will help him stay safe until searchers arrive.

"We are all expecting to see Mike come over the hill behind us and be surprised to see us all here," Herdman's friend Michael Macgregor told reporters earlier this week. "I have no doubt that he can survive out there for weeks."